Vacuum skin packaging and packages

ABSTRACT

An object is packaged in a vacuum skin pack formed by evacuating space between a pair of heat-sealable sheets containing the object and by heat-sealing the sheets to each other about the object. The sheets are pore and cell-free; at least at the sealing surfaces. A multitude of convex protrusions is formed in one of the sheets for providing during the formation of the pack a multitude of collapsible and sealable evacuation channels extending between the sheets. The other of the sheets is heated and the object is provided between the sheets. After the evacuation channels have been formed, the space between the pair of sheets is evacuated essentially only through the latter evacuation channels. The flow of heat from the mentioned one sheet in a direction away from the heated other sheet is inhibited, and peripheral portions of the mentioned one sheet about the object are heated while the flow of heat from said one sheet is being inhibited. The mentioned other sheet is moved tightly against the object being packaged by continued evacuation essentially only through the evacuation channels between the sheets.

United States Patent Krueger et al.

[ 1 Aug. 20, 1974 VACUUM SKIN PACKAGING AND PACKAGES [75] Inventors:Leland Ray Krueger, Garden Grove; Dana Rey Holt, Costa Mesa, both ofCalif.

[73] Assignee: Newport General Corporation,

Costa Mesa, Calif.

[22] Filed: Oct. 19, 1972 [21] Appl. No.: 298,982

[52] US. Cl 206/471, 53/22 A, 53/112 A,

[51] Int. Cl B65d 75/30, B65b 31/02 [58] Field of Search 53/22 A, 112 A;206/80 A [56] References Cited UNITED STATES PATENTS 2,912,805 11/1959Maynard 53/37 3,216,172 11/1965 Piazze 53/22 B 3,634,993 l/l972 Pasco etal 53/22 A 3,694,991 10/1972 Perdue et al 53/22 A Primary Examiner--Travis S. McGehee Attorney, Agent, or Firm-Benoit Law Corporation [57]ABSTRACT An object is packaged in a vacuum skin pack formed byevacuating space between a pair of heat-sealable sheets containing theobject and by heat-sealing the sheets to each other about the object.The sheets are pore and cell-free; at least at the sealing surfaces. Amultitude of convex protrusions is formed in one of the sheets forproviding during the formation of the pack a multitude of collapsibleand scalable evacuation channels extending between the sheets. The otherof the sheets is heated and the object is provided between the sheets.After the evacuation channels have been formed, the space between thepair of sheets is evacuated essentially only through the latterevacuation channels. The flow of heat from the mentioned one sheet in adirection away from the heated other tween the sheets.

17 Claims, 10 Drawing Figures 26 i --23 l i i l Tr 1' L...i 'L..J 2e36-. 38 29 x ,3? 23 x 2 O VACUUM SKIN PACKAGING AND PACKAGESCROSS-REFERENCE TO RELATED APPLICATION Certain subject matter hereindisclosed is claimed in U.S. Patent application Ser.-- No. 256,524,filed May 24, 1972 by Richard L. Levor, as a continuation-in-part of US.Patent application Ser. No. 163,157 now abandoned, entitled Vacuum SkinPackaging and Packages, filed July 16, 1971 by said Richard L. Levor,said patent applications are assigned to the subject assignee, and areherewith incorporated by reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention The subjectinvention relates to packaging and, more specifically, to vaccum skinpackaging and vacuum skin packs.

2. Description of the Prior Art Packaging of goods historically has beena major concern of mankind. Most of this aspect of human history hasbeen spent with the development of better packaging materials. With theprogress of the industrial age, human effort has branched into the questfor better packaging techniques.

A substantial improvement of packaging materials and packagingtechniques came in the wake of the de-' velopment of plastics. Theseefforts have yielded techniques in which containers are vacuumpre-formed for subsequent reception of goods. Even where such containerswere made expandable by a provision of currugations or pleats (see US.Pat. No. 3,497,059), the utility of these techniques still depended onthe uniformity of the shape and size of the goods being packaged.

In other prior-art proposals, the object to be packaged is, in somemanner, placed in an evacuable space. For instance, the object may beinserted into a plastic bag which, in turn, is inserted into a vacuumchamber. Upon evacuation of that chamber, the bag collapses against theobject and can then be sealed. Similar priorart proposals provideconduits, tubes, and the like devices for drawing air out of the bag(see US. Pat. Nos. 2,750,719, 3,010,262, 3,216,832, 3,347,011,3,358,415, 3,481,101).

The major drawback of these proposals is the considerable apparativeeffort involved in providing the requisite vacuum chambers or thespecialized package preforming and holding equipment as well as thespecialized tooling involved in the provision and operation ofevacuation conduits and tubes.

In techniques known as vacuum skin packaging, the object to be packagedis placed on a substrate. A thermally softened plastic skin is movedonto the object and substrate and is drawn against object and substrateby an evacuation step, and is then sealed to the substrate. Themajorstumbling block in the development of practical vacuum skinpackaging techniques has been the evacuation step, since thisnecessitated a removal of gas or gases (typically air) from in betweenthe substrate and top skin. I

A review of prior-art proposals shows that the price so far paid for theevacuation step can only be called exorbitant. In order to evacuate thespace between substrate and top skin, porous or perforated substrateswere used (see US. Pat. Nos. 2,855,735, 2,931,495, 2,989,827, 3,583,129,Canadian Pat. No. 555,219, by

ful porous backing materials are opaque or translucent at best,permitting no or only scattered passage of light, difficulties wereencountered in producing packages through which the packaged objects arevisible from all sides.

In an effort to avoid the drawbacks of porous substrates, the U.S. Pat.No. 3,154,898, by E. F. Engles, issued Nov. 3, 1964, proposed the use ofa heat shrinkable foamed backing, notably a backing or substrate ofpolystyrene foam, polyethylene foam and polyvinyl foam. The idea behindthis proposal probably was that thermoplastic foamed backings would begenerally non-porous because of their closed cell structure. Intensivetests have proved that packages produced according to this proposalprovide no sufficient vapor barrier and little or no effective water ormoixture protection for the packaged goods. In fact, it was found that aconsiderable amount of the air was evacuated through the backing,thereby placing these thermoplastic foam backings into the same class asporous cardboard backings.

In retrospect, these test results are not too surprising, since all goodplastics handbook lists the relatively high water absorption and vaportransmission of foamed plastics. Also, the gas-bubble-permeatedstructure and cellular nature of foamed plastics, even those of theclosed-cell type, does not lend itself to a maintenance of the degree ofnon-porosity required of high-quality food or goods packages.

Tests also indicated that only few plastic materials will provide a heatseal between a backing of a foamed version of the plastic material and atop skin of an unfoamed version thereof. The few plastic materials thatdo seal, generally seal so well that peripheral portions of the packageare sealed before the air around the packaged object is evacuated. Airevacuation then proceeds through the supposedly non-porous backing.

Another effect that was observed in testing heatshrunk thermoplasticbackings was the formation of air inclusions around raised portions ofthe shrunk backing. These air inclusions militate against continuedmaintenance of a sealed package. This also is believed to have been thechief reason for the manifest preference of porous base sheets in theabove mentioned Canadian patent.

That Canadian patent at one point mentions the use of non-porous or butslightly porous coarsely rough or granular or scored backings, referringto coarse glass paper or other granule-coated abrasive paper. With thekind of rigid granules or permanent scores contemplated by the Canadianpatent, air inclusions or imperfect bonds are left about'the granules orat the scores. It is thus not surprising that the Canadian patentreverts to porous backings in the further course of its disclosure.

Another example of prior-art thinking is apparent from the U.S. Pat. No.3,216,172, where air evacuation channels between raisedprojections ordimples are left intack after the evacuation process has been completed,except for a small annular portion which is sealed by a special heatsealing tool. Also, the general arrangement of that prior-art proposalis such that a in porous backings, as may be seen in U.S. Pat. No.

3,583,129. Of course, even small pores render vacuum skin packagesunsatisfactory in many applications.

In U.S. Pat. No. 3,491,504 the space above the wrapping top sheet isevacuated to maintain that top sheet away from the substrate duringevacuation of the space about the object tov be packaged. Top sheet andsubstrate are then sealed and atmospheric pressure is restored above thetop sheet to provide for a wrapping of the object. Evacuation of thespace above the top sheet on the side removed from the objectnecessitates the provision, manipulation and control of special vacuumchambers which vary substantially complicate and increase the cost ofthe packaging process and machinery. Also, the dimensions of extravacuum chambers in practical installations in some manner have to betailored to the typical objects to be packaged, whereby the versatilityof the packaging machine is necessarily limited.

A revealing example of how an industry learns to resign itself to aseemingly insurmountable obstacle is seen in U.S. Pat. No. 3,358,829.That proposal starts out with the use of a perforated or poroussubstrate of cardboard, wood, plastic or polyethylene foam. Recognizingthe above mentioned drawbacks of a perforated or porous substrate, theproposal in question employs or pores.

There thus remains a fillet between the top sheet and the object. Thisfillet extends around the object, typically to its entire height. Thisfillet is, of course, a manifestation of the fact that the space insidethe package has not been substantially evacuated. in the case ofpackaged produce and the like, unsightly juices accumulate in thefillet. The package is vulnerable to damage, since the part of the sheetforming the. fillet is suspended in air, rather than being backed up bythe object. Due to the presence of the fillet the object can shiftaround in the package. Worse yet, the space taken up by the filletdiminishes the width of the seal between top sheet and substrate.

The typical material for vacuum platens in prior-art skin packagingmachines is metal. This provides a heat sink at the substrate whichinitially retards premature sealing where the substrate is non-porous oronly slightly porous. Unfortunately, a metal platen, while cold, willalso retard the desired sealing process. Furthermore, a metal plateneventually brings about premature sealing when the metal platen becomeshot in the course of continuous operation.

Another platen material, such as wood, is tolerated when the sealing isto take place after the wrapping process. This is, for instance, thecase in U.S. Pat. No. 3,024,579 where an acetone bath is used to seal avacuum-drawn package. Premature sealing is thus avoided at the expenseof extra handling steps and potentially inadequate seals.

Although the above mentioned U.S. Pat. No. 3,358,829 does not teach anydeviation from established prior-art practice to use a metal vacuumplaten, the coincidence in that patent of large fillets, with theirabove mentioned disadvantages, and cardboard, wood, plastic andpolyethylene foam backings is in retrospect seen as an illustration of acase of premature sealing of the top sheet and substrate.

SUMMARY OF THE INVENTION In retrospect it may be said that the subjectinvention synergistically combines a first method which retards thesealing between two sheets of the vacuum pack with a second methodwhich, by itself, would promote premature sealing. The two methods arecarefully chosen whereby the first method does not impair, but ratherpromotes, the quality of the evacuation step and of the resulting seal,while the former premature sealing effect of the second method is, bythe synergistic combination, converted to a substantial improvement ofthe resulting seal and thus of the quality of the entire package.

' It is broadly an object of the subject invention to provide novelvacuum skin packaging methods and vacuum skin packs.

It is a further object of the subject invention to provide vacuum skinpackaging methods which avoid the above mentioned disadvantages ofprior-art techniques.

It is a related object of the invention to provide improved vacuum skinpackaging methods and vacuum skin packs in which the formation of air orgas pockets between substrate and top skin and the formation of largefillets are essentially eliminated.

It is a further object of the invention to provide vacuum skin packshaving improved sealing properties.

From one aspect thereof, the subject invention resides in a method ofpackaging an object in a vacuum skin pack formed by evacuating spacebetween a pair of sheets containing the object and sealing the sheets toeach other about the object. This method is characterized by theimprovement comprising, in combination, the steps of providing a pair ofheat-scalable sheets, each being pore and cell-free at least at thesealing surface, forming a multitude of convex protrusions in one ofsaid sheets for providing during the formation of said pack a multitudeof collapsible and sealable evacuation channels extending between saidsheets and being delimited on opposite sides by said sheets, heating theother of said sheets, providing said object between said sheets and saidsheets in proximity to each other, inhibiting the flow of heat from saidone sheet in a direction away from said heated other sheet, evacuatingthe space around said object and between said sheets until saidevacuation channels have been formed and continuing said evacuationessentially only through said evacuation channels while said sheets formgas barriers on said opposite sides, heating peripheral portions of saidone sheet about said object while said flow of heat from said one sheetis being inhibited, moving said other sheet tightly against said objectby continuing said evacuation essentially only through said evacuationchannels, and collapsing said evacuation channels and sealing saidevacuation channels by sealing said sheets to one another.

The expression essentially only as herein employed is intended todistinguish the subject invention from the above mentioned prior-arttechnique in which the space inside the package is evacuated through aporous or cellular backing or through evacuation tubing distinct fromthe sheets.

The expression pore and cell-free refers to a freedom from cells, suchas the cells of foamed plastics or other cellular materials, as well asto a freedom from pores through which significant amounts of air or gaswould be drawn during the evacuation step. No exact dictionaryequivalents could be found for these expressions, so that solid isherein employed for porefree while homogeneous is herein employed forcell-free. Because of their pore and cell-free structure at at least thesealing surfaces, the sheets will form gas barriers on opposite sides ofthe evacuation channels so that no significant amount of gas (air orother gas mixture or gas) can be drawn through either of the sheetsduring the evacuation process.

The expression convex as herein employed is not intended to be limitedto outwardly rounded or curved shapes, but also is meant to coverconfigurations for the protrusions with curved or slanted sides, whereinthe cross-sectional dimension of each protrusion is largest at the baseof the protrusion.

The above mentioned step of collapsing the evacuation channels maytypically be integral with the evacuation process, in that theevacuation channels are advantageously collapsed by pressure generatedby progressive evacuation. In further synergistic operation of the stepsof the inventive method, the inhibition of the mentioned flow of heatand the mentnioned heating of one sheet are effective to bring about notonly a collapse of the evacuation channels, but, if desired, also acollapse of the convex protrusions and a resulting improvement of thesealing effect and quality.

The expression sealing surface used in conjunction with the pore andcellfree condition of each sheet is intended to refer not only to thesurface at which the sheet is actually sealed to the other sheet, butalso to the remainder of the surface which will contact the object. Thisremainder, too, is a potential sealing surface as the size of theobjects to be packaged can be widely varied in accordance with thesubject invention.

That the protrusions providing the evacuation channels are made convexis an essential feature which minimizes a formation of gas pocketsaround or at a location of the protrusions in the sealed package. Thissolves a cumbersome prior-art problem without resort to disadvantageousporous backings.

As to the broad aspect of the invention, no critical limitation isintended with respect to the manner in which the object to be packagedis placed between the sheets and in which the sheets are provided inproximity to each other. For instance, the object may be placed onto oneof the sheets and the other sheet may then be lowered onto the objectand toward the other sheet. Or, the one sheet with the object may beraised toward the other sheet.

A preferred embodiment of this invention includes the step of providingthermal insulation adjacent said one sheet for inhibiting said flow ofheat from said one sheet in a direction away from said heated othersheet to aid said other sheet in heating said peripheral portions ofsaid one sheet.

A further preferred embodiment of this invention includes the step ofdriving heat into said one sheet in a direction toward said other sheetto heat at least peripheral portions of at least said one sheet.

Another preferred embodiment of this invention includes the step ofreflecting thermal radiation into said one sheet in a direction towardsaid other sheet to heat said peripheral portions of said one sheet.

A further preferred embodiment of this invention includes the step ofproviding a heated body adjacent at least said peripheral portions ofsaid one sheet for inhibiting said flow of heat from said one sheet in adirection away from said heated other sheet.

No limitation to anyparticular method of forming the convex protrusionis intended. For instance, the protrusions may be mechanically preformedor vacuumformed prior to the evacuation process. Alternatively, theprotrusions may, for instance, be vacuum formed or otherwise providedduring the packaging process, such as with the aid of an apertured ordeformed platen.

From another aspect thereof, the subject invention resides also inarticles of manufacture made by the methods of the subject invention.These articles of manufacture or vacuum skin packs are superior inquality to prior-art vacuum packs having a porous or cellular backing orlarge fillets, and are at least more economical than the vacuum packsproduced with the aid of special tooling, such as distinct evacuationtubing or special vacuum chambers.

Nevertheless, the articles of manufacture of the subject invention arenot believed fully susceptible to definition in terms of structure, asfar as the inventive features are concerned.

Accordingly, the articles of the subject invention are defined by theirmethod of manufacture.

From yet another aspect thereof, the subject invention resides in vacuumpack apparatus employing the methods of the subject invention.

BRIEF DESCRIPTION OF THE DRAWINGS The subject invention will be morereadily apparent from the following detailed description of preferredembodiments thereof, illustrated by way of example in the accompanyingdrawings, in which like reference numerals designate like orfunctionally equivalent parts, and in which:

FIG. 1 is a section through essential parts of equipment for formingprotrusions in a plastic sheet, together with a diagrammatic showing ofrequisite components, in accordance with a preferred embodiment of thesubject invention;

FIG. 2 is a top view, on a smaller scale, of a fraction of the sheetproduced by the method and equipment of FIG. 1;

FIG. 3 is a section through a vacuum forming apparatus and illustrates apackaging method in accordance with a preferred embodiment of thesubject invention;

FIG. 4 is a section through a vacuum skin pack in accordance with apreferred embodiment of the subject invention;

FIG. 5 is a sectionalized detail view of a modification of the apparatusand method of FIG. 3, in accordance DESCRIPTION OF PREFERRED EMBODIMENTSThe subject invention may be practiced with various types ofheat-scalable top and bottom sheets including, by way of example, sheetsof ionomer resin, such as those sold by E. I. duPont de Nemours &Company under the registered trademark SURLYN, sheets of polyvinylchloride, sheets of polyethylene, or sheets of unsaturated polyesterresin. If desired, either or both of the sheets may be in the form of alaminate.

Suitable laminates may also be formed in a conventional manner byreinforcing thermoplastic sheets with NYLON or other materialspossessing special properties required of the package. NYLON may beincorporated in plastic sheets or laminates for rupture resistance.

According to the subject invention, both sheets are pore and cell-freeat least at the sealing surfaces. 1 According to FIG. 1, a vacuum platen10 has a multitude of apertures 12 leading from a plenum chamber 13 tothe top surface of the platen. A sheet of the desired material, such asan ionomer sheet or another of the above mentioned sheets, laminates orcoextrusions, is placed on the top surface 14 of the platen 10. Thesheet 15 is heated by thermal radiation and/or convection 16 from aconventional heat source 17 until the sheet material softens. By way ofexample, suitable heat sources include infrared heat sources, heatlamps,

forced hot air equipment, and the like.

. A conventional vacuum pump 18, which is connected to the plenumchamber 13, is then actuated. The resulting evacuation of the chamber 13and apertures 12 will draw parts of the sheet 15 into the apertures 12.In this manner, a multitude of protrusions 20 are formed in the sheet15. These protrusions are convex because of the action of air pressureduring the evacuation process on the softened sheet portions at theapertures. Reference may in this connection be had to pages 776 et seq.of the above mentioned Plastics Encyclopedia, containing an article onthermoforming. FIG. 2B of that article shows in dotted lines how avacuum-drawn softened plastic sheet will assume convex configurations.That article also describes various techniques for making articles orprotrusions with slanted sides being within the definition of convexoutlined above.

As shown on a somewhat reduced scale in FIG. 2, the protrusions 20 arespaced from each other to provide a multitude of collapsible andscalable evacuation channels 21 to be more fully described in connectionwith FIG. 3. The protrusions may be offset relative to each other tocontort the evacuation channels 21. For instance, as seen in FIG. 2, theprotrusions 20 are offset relative to each other to provide contortedevacuation channels as seen in a horizontal and in a vertical direction.Contorted evacuation channels have the advantage of diminishing theeffect of local leaks on the evacuation process during formation of thepackage.

As seen in FIG. 3, the sheet 15 is placed on a vacuum platen in aninverted position wherein the protrusions 20 project upwardly. An object22 to be packaged is placed on the sheet 15. As further shown in FIG. 3in dotted outline, a thermoplastic top sheet 23 is inserted and heldbetween top and bottom portions 24 and 25 of a frame structure 26. Thisframe structure may be of a conventional type shown in the abovementioned US Pat. Nos. 2,855,735, 2,989,827 or 3,024,579, allincorporated by reference herein, or the above mentioned Modern PlasticsEncyclopedia issue, at page 567, for instance. The top sheet 23 isheated by the source 17. Upon having attained a sufficient softeningtemperature, the sheet 23 is moved downwardly. This is preferablyaccomplished by moving the frame structure 26 in the direction of thearrows 28 and 29 until the frame structure 26 is in the solidlyillustrated position shown in FIG. 3. Such frame structure movement maybe effected along conventional rails or guides (not shown). It is alsowithin the contemplation of this invention to have the vacuum platen 10move upwardly towards the sheet 23, rather than have the sheet 23 movedownwardly towards the platen.

In the solidly illustrated position, the lower element 25 of the framestructure 26 abuts a vacuum seal 31 around the top of the enclosure 32of the plenum chamber 13. The softened top sheet 23 is draped over theobject 22 as shown in FIG. 3.

In accordance with an essential feature of the subject invention, theflow of heat from the lower sheet 15 in a direction away from the heatedtop sheet 23 is inhibited. In the illustrated preferred embodiment ofFIG. 3, for instance, this is accomplished by the use of thermalinsulation. More particularly, the platen used in the apparatus andmethod of FIG. 3 is made of thermally insulating material, such aslow-density wood, thermally insulating ceramics, natural or syntheticfelt, or various plastics materials. Once the subject invention has beenunderstood, various suitable materials for the platen become apparent tothose skilled in the art. In some of our prototypes we covered thethermally insulating material with a higher-density layer, such as aDacron or Nylon fabric, to protect the insulating core of the platen andfacilitate removal of the formed packs from the platen (see top layer104' shown in dotted outline in FIG. 8).

The activated vacuum pump 18 evacuates the space 34 occupied by andsurrounding the object 22 between the sheets 15 and 23. Theresultingvacuum draws portions of the sheet 23 about the object 22 progressivelydownwardly as indicated by the dotted lines 36, 37, 38 and 39.

in the position indicated by the dotted lines 37 and 38, peripheralportions of the sheet 23 about the object 22 are placed on top portionsof the protrusions 20. Despite this close proximity of the sheets 15 and23, evacuation channels 21 are still provided by the protrusions 20 fromspace adjacent the object 22 to the periphery of the sheet 15.Accordingly, the evacuation provided by the pump 18 progressesessentially only through the latter evacuation channels while the sheets15 and 23 form gas barriers on opposite sides of the evacuationchannels. 2

Peripheral portions of the substrate about the object 22 are heatedwhile the flow of heat from the substrate 15 is being inhibited asherein disclosed. By way of example, peripheral portions of thesubstrate 15 are heated by the source 17 by way of the sheet 23. Unlikethe method of the above mentioned US. Pat. No. 3,358,829 and otherprior-art proposals, the top sheet 23 is moved tightly against theobject 22 by continuing the evacuation essentially only through theevacuation channels 21 (see also FIG. 4). There are no large fillets orother voids about the object 22. Premature sealing between the top sheet23 and substrate 15 is avoided by the protrusions or dimples 20.

The evacuation continuing through the evacuation channels draws top film23 into conformity with the substrate 15. Owing to the curved orlaterally slanted configuration of the convex protrusions 20, an idealconformity between the top sheet 23 and substrate 15 is possible, andair or gas inclusions and imperfect bonds between top sheet andsubstrate are minimized.

The drawing of the top sheet 23'into conformity with the substrate 15progresses continuously toward a sealing of the sheets 15 and 23 to eachother about the object 22. This progressively collapses and closes theevacuation channels 21 until the sheets become sealed to each other atthe end of the evacuation process and throughout the contacting surfacesof the sheets 15 and 23. An interesting effect due to an essentialfeature of the subject invention has been noted in practice. Because ofthe above mentioned inhibition of heat flow from the substrate 15 in adirection away from the top sheet 23, sufficient heat energy is providedand conserved to collapse not only the evacuation channels 21, but, ifdesired, also the protrusions themselves. This improves the quality ofthe resulting seal and vacuum pack very substantially.

By way of summary, it will thus be recognized that the evacuationprocess is prolonged by a retardation of the sealing of the sheets dueto the presence of the protrusions 20. In this manner, a suddencessation of the evacuation process due to a premature contact andsealing of the sheets 15 and 23 is avoided by the subject invention.However, the quality and strength of the resulting seal is at the sametime promoted by the disclosed heat flow inhibition.

The vacuum pump 18 is deactivated after the sheets 15 and 23 have becomeheat sealed to one another at peripheral portions around the object 22.The frame element 24 may then be lifted away from the element 25 and thevacuum skin pack may be removed from the apparatus. Circumferentialportions of the sheets 15 and 23 may be trimmed in a conventionalmanner.

A vacuum skin pack 42 containing the packaged object 22 located on thebacking sheet 15 and provided with an outer skin 43 by the top sheet 23is shown in FIG. 4. The pack 42 has been formed by the method shown inFIG. 3. When a platen 100 having apertures 12 over its area is employedin the method and apparatus of FIG. 3, the upward protrusions 20 aretypically drawn downwardly as indicated in FIG. 4 at 20 during theevacuation and sealing process. On the other hand, when a solid platen101 is employed, the protrusions 20 may be collapsed as mentioned above.The sealed peripheral portions of the substrate 15 and top sheet 23 arethen essentially flat as shown at 44, which may not only improveattainable sealing properties, but also the appearance of the pack 42.

The apertures or channels 12 can be eliminated and a solid platen 101 asin part shown in FIG. 3 may be employed because of the fact thatevacuation takes place according to the subject invention through thechannels 21 provided by the protrusions 20 between and along the sheets15 and 23. In accordance with the principles of the subject invention, asolid platen, moreover, can be used, since the disclosed inhibition ofheat flow enables a collapsing of the protrusions 20 and a smootheningof the peripheral sheet portions. Downward drawing of the protrusions asshown at 20' in FIG. 4 thus becomes unnecessary.

The vacuum skin pack 42 may be described as having two sheets 15 and 23containing at least one packaged object 22 and being sealed to oneanother around the object 22. The sheets 15 and 23 are pore andcell-free at least at the sealing surfaces, including the inner surfaceswhere the sheets contact the object 22. The sheets 15 and 23 haveintimately sealed surfaces where they contact each other and allevacuation channels between the sealed sheets are collapsed and sealed,and the protrusions 20 also may be collapsed and smoothened inperipheral sheet portions.

In the illustrated preferred embodiments, the protrusions 20 are in theform of raised nodes which are spaced from each other to provide theevacuation channels 21. These nodes may also be designated as dimplesand the sheet 15 may be designated as dimpled. The requisite convexprotrusions may alternatively be provided by corrugating or otherwisedeforming either or both of the sheets to form the requisite collapsibleevacuation channels 21. On the basis of practical tests, the provisionof raised, substantially circular nodes is, however, the best modepresently contemplated. Methods and tools other than those shown in FIG.1 (such as dimpled rollers) may be employed for forming the convexcircular nodes or dimples prior to the packaging process or in situ inthe evacuation apparatus.

The sheets 15 and 23 are of light-transparent material if a visibilityof the packaged object 22 from all sides of the pack 42 is desired.

In accordance with a preferred embodiment of the subject invention, thesubstrate 15 is supported by a perforation-free surface while theevacuation channels 21 and the protrusions 20 are collapsed. As aresult, the peripheral package portions are essentially flat as seen at44 in FIG. 4.

According to FIG. 5, a solid platen 103 provides a supporting surface104 of the latter type. In other words, the means for supporting thesheet 15 include a platen 103 having a perforation-free support surfacefor the sheet 15. In FIG. 5, the platen comprises or is of a thermalinsulating material which may be the same as the material of the platen101 of the apparatus of FIG. 3. As shown by way of example in FIG. 5,the

platen 103 is supported by posts 106 and 107.

The enclosure 32 and adjacent parts of the apparatus define evacuationchannels 108 and 109 laterally of the platen 103. The remainder of theapparatus of FIG. 5 may be identical or similar to that of FIG. 3.

As seen in FIG. 6, the requirement that the platen have aperforation-free support surface for the substrate 15 does not excludethe optional presence of marginal perforations. More specifically, thethermally insulating platen 112 of FIG. 6, which may be of the samematerial as the platen 101 or 103, has perforations 113 in marginalregions 114 about the perforation-free support surface 104. Theperforations 1 13 do not essentially impair the perforation-freecharacter of 5 the substrate supporting surface 104, since they areoutside such supporting surface. In this manner, the peripheral portionsof the sheets and 23 will be flat as shown at 44 in FIG. 4.

According to FIG. 7, the above mentioned solid platen 101 (or one of theother perforation-free platens disclosed herein) is provided with alayer of reflective inhibiting the flow of heat from the substrate 15 ina direction away from the top sheet 23, since the layer 116 reflects thethermal radiations back into the substrate 15 in a direction toward thetop sheet 23.

According to FIG. 8, a metal supporting platen 121 vmay be employed inlieu of the platen 101, 103 or 112 'of thermally insulating material.The requisite means for inhibiting the flow of heat from the substrate15 then include a layer of insulating material 123. The layer 123 may beof the same material as theplaten In the preferred embodiment of FIG. 8,the perforation-free surface 104 for supporting the substrate 15 isformed or, defined by the layer 123.

According to FIG. 9, a platen 131 includes means 132 for heating theplaten. The platen 131 may be used instead of the platen 101, 103, 112or 121 in the embodiment of FIGS. 3, 5, 6, 7 or 8. The heating means 132heat the platen 131 to a temperature at which flow of heat from thesubstrate 15 in a direction away from the top sheet 23 is inhibited. Forinstance, the heating means 132 may heat the platen to a temperaturewhich is higher than, or equal to, the temperature to which thesubstrate 15 is heated by heat from the heated top sheet 23. a

As shown in FIG. 9, the heating means 132 may include an electricalheating element 134 which is energized by way of a potentiometer 136 byan electric power source 137. This renders adjustable the temperature ofthe platen 131.,

The heated platen 131 may be of metal or it may, as before, be of athermally insulating material. The perforation-free surface 104 forsupporting the substrate 15 may be provided by the heated platen itself,or by a sheet of insulating material 123 which is located on the platenas shown in FIG. 8.

According to FIG. 10, the packaging process is carried out in a specialgas atmosphere. To this end, a supply 47 of an inert gas such as carbondioxide or nitrogen or highly reactive gas such as ethylene oxide, forinstance, is connected to the plenum chamber 13 by a valve 48. There areseveral possible methods by means of which the gas from the supply 47may be provided in the space 34 between the sheets 15 and23. In onepreferred embodiment, the space 34 (see FIG. 3) is first pre-evacuatedby the pump 18 and the valve 48 is then opened so that the gas from thesupply 47 will permeate the space 34. Alternatively, the space betweenthe'sheets l5 and 23 may be flushed with the desired gas shortly beforethe frame structure 27 has moved downwardly past the platen 10. Ineither case, at least a portion of the gas is evacuated through thechannels 21 prior to sealing.

The scope of the present invention extends also to methods in which atleast one of the sheets is preformed in the manner known, for instance,from conventional blister packs. In that case, the sealing of the topsheet 23 to the backing sheet 15 may generally proceed in the mannerdescribed above.

Various other modifications within the spirit and scope of the subjectinvention will suggest themselves or become apparent from the subjectdisclosure to those skilled in the art.

I claim: 1. In a method of packaging an object in a vacuum skin packformed by evacuating space between a pair of sheets containing saidobject and sealing said sheets to each other about said object, theimprovement comprising in combination the steps of:

providing a pair of heat-sealable sheets, each being pore and cell-freeat least at the sealing surface;

forming a multitude of convex protrusions in one of said sheets forproviding during the formation of said pack a multitude of collapsibleand sealable evacuation channels extending between said sheets and beingdelimited on opposite sides by said sheets;

heating the other of said sheets;

providing said object between said sheets and said sheets in proximityto each other;

inhibiting the flow of heat from said one sheet in a direction away fromsaid heated other sheet; evacuating the space around said object andbetween said sheets until said evacuation channels have been formed andcontinuing said evacuation essentially only through said evacuationchannels while said sheets form gas barriers on said opposite sides;

heating peripheral portions of said one sheet about said object whilesaid flow of heat from said one sheet is being inhibited; moving saidothersheet tightly against said object by continuing said evacuationessentially only through said evacuation channels; and collapsing saidevacuation channels and sealing said evacuation channels by heat-sealingsaid sheets to one another. 2. A method as claimed in claim 1, includingin said combination the step of:

providing thermal insulation adjacent said one sheet for inhibiting saidflow of heat from said one sheet in a direction away from said heatedother sheet. 3. A method as claimed in claim 1, including in saidcombination the step of: 5

driving heat into said one sheet in a direction toward said other sheetto heat said peripheral portions of said one sheet. 4. A method asclaimed in claim 1, including in said combination the step of:

reflecting thermal radiations into said one sheet in a direction towardsaid other sheet to heat said peripheral portions of said one sheet. 5.A method as claimed in claim 1, including in said combination the stepof:

providing a heated body adjacent at least said peripheral portions ofsaid one sheet for inhibiting said flow of heat from said one sheet in adirection away from said heated other sheet.

6. A method as claimed in claim 1, wherein:

said provision of said object between said sheets includes the steps oflocating said object on said one sheet and draping said heated othersheet over said object.

7. A method as claimed in claim 1, wherein:

both of said sheets are made of light transparent material.

8. A method as claimed in claim 1, wherein:

the sealing of said sheets to each other about said object is retardedby said protrusions to prolong the evacuation of said space; and

said sealing of said sheets to one another is intensified by saidinhibition of said flow of heat to improve the resulting seal betweensaid sheets.

9. A method as claimed in claim 8, wherein:

said convex protrusions are collapsed in said peripheral portions ofsaid one sheet with the aid of heat flowing from said heated other sheetwhile said flow of heat from said one sheet is inhibited.

10. A method as claimed in claim 1, wherein:

said convex protrusions are collapsed in said peripheral portions ofsaid one sheet with the aid of heat flowing from said heated other sheetwhile said flow of heat from said one sheet is inhibited.

11. A method as claimed in claim 10, wherein:

said one sheet is supported by a perforation-free surface while saidevacuation channels and said protrusions are collapsed.

12. A method as claimed in claim 1, wherein:

said protrusions are provided by forming a multitude of convex raisednodes in said one sheet, said nodes being spaced from each other toprovide said evacuation channels.

13. A method as claimed in claim 12, wherein:

said raised nodes are offset relative to each other to contort saidevacuation channels.

14. A method as claimed in claim 1, wherein:

said space is provided with a substantially inert atmosphere prior toevacuation thereof.

15. A vacuum skinpack containing at least one packaged object andcomprising two sheets sealed to one another around said object and beingpore and cell-free at least at surfaces where said sheets are sealed andat inner surfaces where said sheets contact said object, said vacuumskin pack having been made by a method as claimed in claim 1.

16. A vacuum skin pack as claimed in claim 15, wherein:

the sealing of said sheets to each other about said object is retardedby said protrusions to prolong the evacuation of said space; and

said sealing of said sheets to one another is intensified by saidinhibition of said flow of heat to improve the resulting seal betweensaid sheets.

17. A vacuum skin pack as claimed in claim 15, wherein:

said sheets have essentially flat sealed peripheral portions around saidobject.

1. In a method of packaging an object in a vacuum skin pack formed byevacuating space between a pair of sheets containing said object andsealing said sheets to each other about said object, the improvementcomprising in combination the steps of: providing a pair ofheat-sealable sheets, each being pore and cell-free at least at thesealing surface; forming a multitude of convex protrusions in one ofsaid sheets for providing during the formation of said pack a multitudeof collapsible and sealable evacuation channels extending between saidsheets and being delimited on opposite sides by said sheets; heating theother of said sheets; providing said object between said sheets and saidsheets in proximity to each other; inhibiting the flow of heat from saidone sheet in a direction away from said heated other sheet; evacuatingthe space around said object and between said sheets until saidevacuation channels have been formed and continuing said evacuationessentially only through said evacuation channels while said sheets formgas barriers on said opposite sides; heating peripheral portions of saidone sheet about said object while said flow of heat from said one sheetis being inhibited; moving said other sheet tightly against said objectby continuing said evacuation essentially only through said evacuationchannels; and collapsing said evacuation channels and sealing saidevacuation channels by heat-sealing said sheets to one another.
 2. Amethod as claimed in claim 1, including in said combination the step of:providing thermal insulation adjacent said one sheet for inhibiting saidflow of heat from said one sheet in a direction away from said heatedother sheet.
 3. A method as claimed in claim 1, including in saidcombination the step of: driving heat into said one sheet in a directiontoward said other sheet to heat said peripheral portions of said onesheet.
 4. A method as claimed in claim 1, including in said combinationthe step of: reflecting thermal radiations into said one sheet in adirection toward said other sheet to heat said peripheral portions ofsaid one sheet.
 5. A method as claimed in claim 1, including in saidcombination the step of: providing a heated body adjacent at least saidperipheral portions of said one sheet for inhibiting said flow of heatfrom said one sheet in a direction away from said heated other sheet. 6.A method as claimed in claim 1, wherein: said provision of said objectbetween said sheets includes the steps of locating said object on saidone sheet and draping said heated other sheet over said object.
 7. Amethod as claimed in claim 1, wherein: both of said sheets are made oflight transparent material.
 8. A method as claimed in claim 1, wherein:the sealing of said sheets to each other about said object is retardedby said protrusions to prolong the evacuation of said space; and saidsealing of said sheets to one another is intensified by said inhibitionof said flow of heat to improve the resulting seal between said sheets.9. A method as claimed in claim 8, wherein: said convex protrusions arecollapsed in said peripheral portions of said one sheet with the aid ofheat flowing from said heated other sheet while said flow of heat fromsaid one sheet is inhibited.
 10. A method as claimed in claim 1,wherein: said convex protrusions are collapsed in said peripheralportions of said one sheet with the aid of heat flowing from said heatedother sheet while said flow of heat from said one sheet is inhibited.11. A method as claimed in claim 10, wherein: said one sheet issupported by a perforation-free surface while said evacuation channelsand said protrusions are collapsed.
 12. A method as claimed in claim 1,wherein: said protrusions are provided by forming a multitude of convexraised nodes in said one sheet, said nodes being spaced from each otherto provide said evacuation channels.
 13. A method as claimed in claim12, wherein: said raised nodes are offset relative to each other tocontort said evacuatioN channels.
 14. A method as claimed in claim 1,wherein: said space is provided with a substantially inert atmosphereprior to evacuation thereof.
 15. A vacuum skin pack containing at leastone packaged object and comprising two sheets sealed to one anotheraround said object and being pore and cell-free at least at surfaceswhere said sheets are sealed and at inner surfaces where said sheetscontact said object, said vacuum skin pack having been made by a methodas claimed in claim
 1. 16. A vacuum skin pack as claimed in claim 15,wherein: the sealing of said sheets to each other about said object isretarded by said protrusions to prolong the evacuation of said space;and said sealing of said sheets to one another is intensified by saidinhibition of said flow of heat to improve the resulting seal betweensaid sheets.
 17. A vacuum skin pack as claimed in claim 15, wherein:said sheets have essentially flat sealed peripheral portions around saidobject.